Relations Between Biomass Indices And Soil Carbon Deposition Of Larch Plantations

In despite of many researches on relations between biomass carbon and tree growth, the similar soil organic carbon (SOC) relations were rarely surveyed and conclusions are also controversial to date. Through the clarification of these growth-related differences between biomass and SOC, we tried to explore some simple indicators for identifying the changes of SOC during forest development. An investigation was carried out on the biomass, aboveground litter mass and SOC dynamics of139chronosequence plots of larch plantation forests in NE China. Our results showed that:1) Change of biomass indices with plantation age. Significant linear correlations between larch body size (DBH:diameter at breast height, tree height and plant biomass) and tree age were observed (p<0.001). Similarly, significant increases in stand biomass density (biomass per one unit area of soil) with tree age were also observed (R2=0.35-0.6, p<0.001); Surface litter mass was quadratically related with tree age, i.e., obvious escalation before the age of37, but decrease thereafter was observed (p<0.05). Other growth parameters, such as DBH, tree height, tree size as well as biomass density were linearly correlated with the litter mass above soil surface (R2=0.14-0.82, p<0.001), and the best correlation was found in tree height. Thus, tree height should be the optimal parameter to evaluate the changes of litter mass in larch plantations.2) Relations between biomass accumulation and soil organic carbon. The deep soil organic carbon (40-60cm and60-80cm) was significant decreasing with plantation age, surface soil did not change significantly (p>0.05). DBH, tree height was significantly correlated with deep soil organic carbon (60-80cm). The SOC of40-80cm was negatively correlated with ground part size and the root system size. SOC ratio between0-40cm and40-80cm increased significantly with plantation age (p<0.01). The tree size parameters were significantly negatively correlated with deep SOC, and the ratio between surface and deep soil SOC also displayed a significant upward trend with increasing DBH and tree height (p<0.05). Owing to the fact that SOC in deep soil is more stable than that in surface, the increase of SOC ratio indicates that more SOC may accumulate in surface layer, and this will be a risk of soil carbon return atmosphere.3) Some biomass accumulation rate indices had a better indicate fiction for soil organic carbon. Along with the increasing of plantation age, the content and storage of deep soil organic carbon (40-60cm and60-80cm) were significant decreasing, surface soil did not change significantly (p>0.05). There was no correlation between DBH and parameters such as content and reserves of SOC. DBH growth rate and the soil organic carbon content of20-40 cm,40-60cm,60-80cm,0-80cm soil layer had a significant positive correlation. There was no correlation between tree height and SOC content and storage. Tree height growth rate had a significant impact on soil organic carbon content of0-20cm,20-40cm,40-60cm,60-80cm soil layers. Soil organic carbon storage of40-60cm and biomass growth rate had a significant positive related.Through the analysis difference between various biomass index and different physical and chemical properties of soil layer, our results showed that correlation coefficient between tree height growth rate and physical and chemical properties was highest (R2=0.042) in0-20cm soil layer; and in the20-40cm soil layer the influence of physical and chemical properties and plantation age was significantly higher than other index; in40-60cm soil layer correlation coefficient between tree height growth rate and physical and chemical properties was highest; in the60-80cm the correlation coefficients between DBH growth rate and physical and chemical properties was the highest (R2=0.05).Correlation coefficients between tree height growth rates and soil organic carbon, total nitrogen, total phosphorus, total potassium content were significantly higher than other indicators. P-value number of tree height growth rate and the elements content which had reached significantly (n=13) were higher than that the storage (n=8).Correlation coefficient between tree height growth rate and soil physical and chemical properties of different layer was0.06, which was significantly higher than other biomass indicator. P-value number of tree height growth rate and soil physical and chemical properties which had reached significantly was25. Tree height growth rate was a credible parameter to describe carbon changes.